Various applications involve identifying and displaying geographical map locations. An exemplary application is a mobile navigation application that presents navigational information to a mobile user. Several mobile navigation systems and methods are known in the art. For example, U.S. Pat. No. 6,917,878, whose disclosure is incorporated herein by reference, describes a method for navigation that includes storing map data on a server. The map data includes vector information delineating roads in a map. A portion of the vector information corresponding to an area in which a user of a mobile client device is traveling is downloaded from the server to the client device. Approximate position coordinates of the user are found using a location-providing device associated with the client device. The approximate coordinates are corrected in the client device using the downloaded vector information, so as to determine a location of the user on one of the roads in the map. A navigation aid is provided to the user of the client device based on the determined location.
As another example, U.S. Pat. No. 6,898,516, whose disclosure is incorporated herein by reference, describes a method for displaying a map on a mobile client device. The method includes storing map data on a server, the map data defining objects appearing in the map and comprising vector coordinates of the objects in a predetermined frame of reference. Upon receiving at the server a request from the client device to provide a map of an area along a route on which a user of the client device is to travel, a heading of travel of the user on the route is determined, and the vector coordinates are transformed on the server into a rotated frame of reference, which is approximately aligned with the heading of the user. A portion of the map data corresponding to the area along the route and including the transformed vector coordinates is downloaded to the client device from the server. An image of the area of the map in the rotated frame of reference is rendered on the client device, based on the downloaded map data.